What is wrong with a dog when it sticks its tail between legs?

When a dog sticks its tail between its legs, it usually indicates that the dog is feeling fearful, submissive, or anxious. Sticking the tail between the legs is a natural defence mechanism that dogs have developed over time to show that they are not a threat to other dogs or predators. It can also be a sign of pain or illness, so it's important to look at the dog's overall body language and behaviour to determine the reason for the tail being tucked in.